Tohatsu/Mercury 8, 9.8, 9.9, 15, 18 and 20 4S.. whats what?

[km1125]

Ok, I know that some years (98-2003ish) the 9.9, 15 and 18 were the same motor, with the exception of carb and cam

It appears at some point they made a 9.9 version of the 8HP but then made the 9.8. Then about that time they dropped the 18 and then the 15 and the 20 were the same, except for carbs. Was there another 9.9 that's different than the one above (the 9.9/15/18)? What years was it produced and was it the same block/internals as the 8, or a completely different motor?

Can someone spell out a rough timeline and which engines are part of the same family (same block/internals)?

Thanks

 

[Scott Danforth]

start by looking at the parts diagrams

 

[pvanv]

Tohatsu made all Nissans. Makes all current Mercs 30 and down. Makes all Evinrudes 20 and down.
The 8/9.8 2-st were in the same family. Same is now true of the 4-strokes.
When the 4-stk 9.8 came out, they dropped the 9.9/15/18, and the 15/20 came out.
Now, the 9.9/15/20 EFI is out.
The 8 was never the same as a 9.9.